We are using the isoenzymes of aldolase and several other enzymes as well defined "marker" proteins to investigate the regulatory mechanisms responsible for controlling the levels of specific proteins in animal cells. Our work should clarify the detailed regulatory event which (1) determine the steady state concentrations of these proteins in tissues of adult animals, (2) establish the steady state levels of these molecules during the process of cellular differentiation, and (3) cause the changes in levels of specific proteins in disease states such as diabetes and muscular dystrophy. The regulatory events are being investigated using whole animal systems, tissue explants in culture, and cell-free protein synthesizing systems.